The goal of the proposed research is to understand the cellular molecular mechanisms by which DNA damage is processed to give stably inherited mutations. The drug-resistance plasmid, pKM101, causes a striking enhancement of radiation and chemical mutagenesis when present in bacterial screening strains used to detect carcinogens and mutagens. Results to date have suggested that pKM101 enhances mutagenesis and increases resistance to UV killing by coding for functions involved in the hypothesized "error-prone repair" functions and this relationship will be further explored. The genetics of the system will be characterized by the isolation and analysis of mutations in both plasmid and chromosomal genes involved in the processs. Smaller derivatives of pKM101 will be obtained by restriction-enzyme methodology. The plasmid-coded proteins responsible for the enhancement of mutagenesis will be identified. The biochemical basis of the action of pKM101 will be explored and its relationship to known DNA repair pathways will be determined. The physiology and base-pair specificity of the pkM101-mediated processes will be determined. The Esherichia coli umuC gene will be cloned and analyzed in a similar fashion. An in vitro system will be developed to study the biochemistry of chemical mutagenesis. Results of these studies will be applied to improving bacterial screening systems for carcinogens. It is hoped that elucidation of the molecular mechanisms of chemical mutagenesis in enteric bacteria will provide a model for similar processes in eucaryotes and will lead to an understanding of the origin of diseases such as cancer.